RE: [PATCH] static_call,x86: Robustify trampoline patching

David Laight
2021-11-01T09:36:37Z

From: Peter Zijlstra
> Sent: 01 November 2021 09:02
..
> In any case, I really want the discussion to start at square one, and
> show/explain why any chosen CFI scheme is actually good for the kernel.
> Just because clang happened to have implemented it, doesn't make it the
> most suitable scheme for the kernel.

How much overhead does it add to write("/dev/null", "", 1) ?
You've two large jump tables.
One for the syscall entry - (all the syscalls have the
same prototype), and a second for selecting the correct
device driver's 'write' entry point.

You really don't want to be doing any kind of search.

Hardware that supported a (say) 16-bit constant in both the
'landing pad' and call indirect instruction and trapped if
they differed would be useful - but I doubt any hardware
that checks landing pads is anywhere near that useful.

David.

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